1. Field of the Invention
This invention relates generally to graphic camera/platemaker optical systems, and, more particularly, to a method and apparatus for extending the magnification/reduction range and allowing greater access to the copyboard at higher magnifications. The method and apparatus further provides for movement of the lens, mirror and copyboard which maintains alignment of the lead edge of the original with the lead edge of the image for different magnifications.
Heretofore, graphic camera/platemaker optical systems with a copyboard for the original subject, a mirror, a lens and an image plane for producing images or reproductions of the original in a variable magnification/reduction scale have been known. In order to reproduce the original in a reduced or enlarged scale, the subject distance and the image distance are changed relative to the lens. To accomplish this, the relative positions of the optical elements of the graphic camera are changed in order to adjust the magnification/reduction scale.
Traditionally, graphic camera/platemaker optical systems have been designed such that the lens and copyboard are movable for the purpose of changing the image size in order to reproduce an original in a variable magnification/reduction scale. The mirror movement in these systems has been in one of the following three ways. The mirror has been fixed to the lens, thereby moving with it to create a linearly varying center on the copyboard such that copy location is non linear with respect to the lead edge of the image as magnification changes. Alternatively, the mirror has been fixed in space creating a fixed center on the copyboard with a non linear lead edge of the image. Finally, the mirror has been connected to the lens by a cam so that it moves in concert with the lens, that is, along the same center line as the lens, creating a non linearly varying center on the copyboard with a non linear lead edge relative to the image.
A camera similar to the graphic camera/platemaker optical system is the repographic camera shown in U.S. Pat. No. 4,253,763, issued to Schleifenbaum. This patent teaches that although the copyboard, lens and the image plane may all be constructed so as to be movable for the purposes of reproducing the original to a different scale, generally one of the components -- usually the image plane -- is held in a fixed position, and only the other two components (lens and copyboard) are linearly displaced. Specifically, this patent teaches that the lens is displaceable linearly along a guide, while the copyboard is movable up and down along a guide. Both the mirror and the image plane remain fixed.
One of the disadvantages with the traditional graphic.cameras is that the position of the mirror establishes the magnification/reduction range for a particular focal length lens. The mirror in the traditional graphic cameras is either fixed in space or to the lens or connected to the lens so that it moves in concert with the lens, that is, along the same track as the lens. Such mirror positioning may preclude the use of larger copyboards and shorter focal length lenses which are suitable for greater reduction ranges. With shorter focal length lenses, the mirror would be moved toward the image plane and it could not project a large enough image from the copyboard.
The mirrors in such arrangements further limit access to the copyboard at higher magnifications by interfering with an operator's ability to open the copyboard cover. When using a platemaker, it is important for the operator to place an original accurately on the copyboard, at every magnification. At higher magnifications, the copyboard is raised to a point closer to the lens. Mirrors fixed in space or attached to the lens are positioned such that they block opening of the copyboard cover, thereby preventing the operator from placing an original accurately on the copyboard. As a result, the graphic camera can not operate effectively since the operator can not accurately place the lead edge of the original at the same distance from the head of the plate at these higher magnifications.
Other optical systems also teach changing image size by moving the optical elements. However, these systems also do not teach that the mirror can be moved independently of the lens in a manner that would avoid the problems in the traditional graphic cameras caused by the mirror which is either fixed in space or attached to the lens. For example, U.S. Pat. No. 4,451,142, issued to Takenaka et al., relates to a photographic system used for printing an original image on a photosensitive material such as enlarger, process camera, copying camera, etc. This patent discloses that conventional photographic apparatus such as enlargers are designed so that an easel holding a photosensitive material and a lens can move vertically along a stay. When the easel is in a desired position, the lens travels automatically to a position determined by the lens formula to focus an image o the photosensitive material.
U.S. Pat. No. 4,488,804, issued to Takagi, discloses a method and machine for automatic focusing in a projection system with continuously variable magnification, wherein an original picture is projected onto a photosensitive material by a focusing lens. One of these three members is fixed and the other two members are adapted to be moved in a direction of a light axis.